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c_ur_f8

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Exchange 2003 - Some SMTP messages not leaving the queue

I have a somewhat new server running (approx 1 month) Exchange 2003 and the problem I'm having is that some of our e-mails are not leaving the queue.  If this is a DNS issue, what would cause some messages to stick and what should I do to fix this issue?  If you can think of another possibility, I'd really like to hear it.  If you need more details, please let me know.

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Sembee
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Any pattern to the domains?

Check whether your DNS is configured correctly http://www.amset.info/exchange/dnsconfig.asp

Simon.
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c_ur_f8

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DNS isn't the problem and after a little more research, it would seem that others are having problems with one of the domains we're trying to hit.  The domain is videotron.ca and their MX record shows them at mx.videotron.ca.  It is here that I can telnet on port 25, but not the videotron.ca alone.  Is there a way I can manually modify my system to recognize this domain for SMTP?
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Sembee
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Why would I be getting a 452 Try Later error when telnetting to mx.videotron.ca 25?
Could be a greylisting.
That is where the server tells you to go away for a while, but when you connect again, lets you deliver the message. It is one of the more recent spam management tools, the theory being that spammers are fly-by-night and will not try and deliver their message again.

Unfortunately it is not always deployed correctly and the message can be misinterpreted by certain servers or send the wrong message and the messages end up in the queues.
I don't use greylisting myself as I find it a bit hit and miss.

Simon.
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Thanks Simon!